A plasma display panel (hereinafter referred to simply as “PDP”), among other flat panel displays (FPD), allows achieving a high-speed display as well as a large-size display with ease. The PDP is thus commercialized in various fields such as video display devices and display devices for public communication.
In general, an AC-drive and surface discharge type PDP adopts 3-electrodes structure, and is formed of two glass substrates, i.e. a front panel and a rear panel confronting each other with a given space therebetween. The front panel includes display electrodes formed of scan electrodes and sustain electrodes, both of which are shaped like stripes and formed on the glass substrate, a dielectric layer covering the display electrodes and storing electric charges for working as a capacitor, and a protective film formed on the dielectric layer and having a thickness of approx. 1 μm. The rear panel includes multiple address electrodes formed on the other glass substrate, a primary dielectric layer covering the address electrodes, barrier ribs formed on the primary dielectric layer, and a phosphor layer painted onto display cells partitioned by the barrier ribs for emitting light in red, green and blue respectively.
The front panel confronts the rear panel such that its electrode-mounted surface confronts an electrode-mounted surface of the rear panel, and peripheries of both the panels are sealed in an airtight manner to form a discharge space therebetween, and the discharge space is partitioned by the barrier ribs. The discharge space is filled with discharge gas of Neon (Ne) and Xenon (Xe) at a pressure ranging from 53 kPa to 80.0 kPa. The PDP allows displaying a color video through this method: Voltages of video signals are selectively applied to the display electrodes for discharging, thereby producing ultra-violet rays, which excite the respective colors of the phosphor layers, so that colors in red, green, and blue are emitted, thereby achieving the display of a color video (Refer to Patent Document 1).
The protective layer formed on the dielectric layer of the front panel of the foregoing PDP is expected to carry out the two major functions: (1) protecting the dielectric layer from ion impact caused by the discharge, and (2) emitting primary electrons for generating address discharges. The protection of the dielectric layer from the ion impact plays an important role for preventing a discharge voltage from rising, and the emission of primary electrons for generating the address discharges also plays an important role for eliminating a miss in the address discharges because the miss causes flickers on videos.
To reduce the flickers on videos, the number of primary electrons emitted from the protective layer should be increased. For this purpose, silicon (Si) or aluminum (Al), for instance, is added to MgO.
In recent years, the number of high-definition TV receivers has increased, which requires the PDP to be manufactured at a lower cost, to consume a lower power, and to be a full HD (high-definition, 1920×1080 pixels, and progressive display) with a higher brightness. The characteristics of emitting electrons from the protective layer determine the picture quality, so that the control over the electron emission characteristics is vital for the picture quality.
In such a PDP, an attempt to improve the electron emission characteristic by making impurity mixed in a protective layer was made (Patent Document 2). However, in the case where impurity is mixed in the protective layer to improve the electron emission characteristic, simultaneously, charges are accumulated on the surface of the protective layer, and the attenuation rate that charges when used as a memory function decrease with time increases. Consequently, a countermeasure to increase application voltage is needed for suppressing the attenuation rate.
As described above, there is a challenge to satisfy two conflicting characteristics of the protective layer; high electron emission capacity, and low attenuation rate of charges as the memory function, that is, high charge retention characteristic.
[Prior Art Document]
[Patent Document]
    [Patent Document 1] Unexamined Japanese Patent Publication No. 2007-48733    [Patent Document 2] Unexamined Japanese Patent Publication No. 2002-260535